1. Field of the Invention
This invention relates generally to semiconductor memory circuits and, more particularly, to an insulated gate field effect transistor (IGFET) quasi-static decoder for programming a dynamic electrically programmable read only memory (EPROM).
2. Description of the Prior Art
Some read only memories may be programmed by causing a permanent and irreversible change in the memory mental interconnection pattern by applying electrical pulses thereto. Other ROMs have been programmed by causing a reversible change in the characteristic of a memory device within the ROM. These so-called alterable ROMs are generally deprogrammed by exposing the device to ultraviolet light. Both static and dynamic decoders have been employed to accomplish this reversible programming; however, each suffer from certain disadvantages.
In the case of a static decoder, the decoder circuitry is configured so as to draw current all the time. With the ever increasing demands for larger and larger memory arrays, the power requirements become very high. Furthermore, static decoders perform at relatively low speeds when compared to dynamic decoders.
While dynamic decoders require less power and perform at higher speeds, they are susceptible to leakage at the precharged nodes. Since it may take as much as 50 milliseconds to program a memory cell, periodic program pulsing is required to overcome the leakage problem. Furthermore, those EPROMs which are ultra-violet erasable are generally equiped with a clear lid. This permits optical infiltration which causes the nodes to discharge even faster.